1. Field of the Invention
The present invention relates to a method of providing semiconductor wafers each having a plurality of bumps exposed from its resin coating.
2. Related Arts
Usually a bare chip is mounted to a package having almost same size as the bare chip like a chip size package (abbreviated as CSP), or it is mounted to a printed circuit board as a flip chip. Such a bare chip has bumps formed on its surface for making required electric connections to the electrodes of a package or printed circuit board. Usually the bumps of a bare chip are soldered to selected electrodes in the printed circuit board, and then, the space in which the bump-to-electrode connections are made between the bare chip and the printed circuit board is filled with resin material, thereby fastening the bump-to-electrode connections both to the bare chip and the printed circuit board.
Recently in the semiconductor industry there has been a technical development in which bare chips are formed like CSPs by coating the semiconductor wafers with a resin material. Semi-fabricated products have their bumps embedded in resin material, and therefore, such coating material needs to be removed until the bumps have been exposed.
A grinding wheel having pulverized grindstone fixed on its surface is used in cutting semiconductor wafers of silicon or the like. When such a grinding wheel is used in removing resin coating from the semi-fabricated products, disadvantageously it is likely that the resin coatings become irregular due to plucking or that a burr causes at the edge of the bump. Therefore, it is difficult to provide complete bare chips having clear-cut bumps exposed on their smooth, even resin coatings.
Also, disadvantageously the resin material is so sticky that particle-to-particle spaces in the grinding wheel surface are stuffed with resin debris, thus preventing the grinding wheel from being used continuously.
One object of the present invention is to provide a method of grinding semi-fabricated semiconductor wafer products having bumps embedded in their resin coatings to remove partly their resin coatings until the underlying bumps have been exposed without causing burrs on the bumps and/or without damaging the surrounding resin coatings due to plucking.
Another object of the present invention is to provide a grinding wheel for use in grinding semi-fabricated semiconductor wafer products having bumps embedded in their resin coatings, which grinding wheel can be used continuously.
To attain these objects a method of providing semiconductor wafers each having a plurality of bumps exposed from its resin coating by using a grinding machine including at least a rotary chuck table for holding a semiconductor wafer having a plurality of bumps embedded in its resin coating and a grinding unit having a rotary wheel held in confronting relation with the rotary chuck table, thereby removing the resin material from the semiconductor wafer until its bumps have been exposed is improved according to the present invention in that: it comprises the steps of: attaching to the grinding unit a rotary wheel having at least one cutter blade formed thereon; holding a semiconductor wafer having a plurality of bumps embedded in its resin coating on the rotary chuck table; positioning the wheel relative to the chuck table so that the cutter blade of the wheel may traverse the center of the chuck table when the wheel is rotated; rotating the chuck table; and rotating the wheel to remove the resin coating from the semiconductor wafer until the bumps have been exposed.
The chuck table and the cutting wheel may be rotated in one and same direction. The rotating speed ratio of the chuck table to the cutting wheel may be 1 to 100 or more. The rotating speed of the cutting wheel may be 3000 or more revolutions per minute whereas the rotating speed of the chuck table may be 10 or less revolutions per minute. The cutter blade may be of diamond or super-hard metal.
A cutting wheel for use in providing semiconductor wafers each having a plurality of bumps exposed from its resin coating is improved according to the present invention in that the cutting wheel has at least one cutter blade on its circumference.
According to the method of grinding semi-fabricated semiconductor wafer and the grinding wheel of the present invention, the resin coatings are removed by grinding with a cutter blade, and therefore it can provide semiconductor wafers having clear-cut bumps in their even resin coating surfaces without causing irregular ends of the resin coatings due to plucking and burrs at the edge of the bumps, thereby increasing quality of the semiconductor wafer.
Further, advantageously the grinding wheels can be used all the time without being stuffed with resin debris, thereby increasing manufacturing efficiency.